It is known to coat medical devices, e.g. catheters for introduction into human cavities such as blood vessels, digestive organs and the urinary system, with a hydrophilic coating, at least on the surface of the insertable part which is introduced or comes into contact with mucous membranes, etc., during introduction of the device. An advantage with such a hydrophilic coating is that it becomes extremely slippery when it is swelled with water, preferably immediately before introduction into the human body and thus ensures a substantially painless introduction with a minimum of damage on tissue.
A large number of methods are known for the production of hydrophilic surface coatings. A known hydrophilic coating process is e.g. disclosed in EP 0 093 093, where isocyanate is used to form a polyurea network for connecting hydrophilic PVP to the substrate. Further, EP 0 217 771 describes a method of adding an osmolality increasing compound to such a hydrophilic coating in order to improve the water retention properties and low friction of the coating. Further, WO 98/58989 discloses a hydrophilic coating which is cross-linked by means of irradiation, and incorporating a water soluble osmolality increasing compound therein.
However, despite adherence to sterile guidelines etc, the use of medical devices, and in particular introduction of medical devices into natural and artificial body openings, implies a risk of bacterial contamination. For example, insertion and maintenance of urinary catheters poses a problem in relation to catheter-associated infections. When medical devices such as a catheter is introduced into the human cavity, the normal human defense barrier may be penetrated, which can result in introduction of bacteria, fungi, vira, or tissue-like or multiple organized cells. Urinary tract infection (UTI), for instance, is a problem associated with the use of urinary catheters, including hydrophilic catheters with hydrophilic coatings for intermittent use. It is estimated that almost one-quarter of hospitalized spinal cord-injured patients develop symptomatic UTI during their hospital course. Gram-negative bacilli account for almost 60-70%, enterococci for about 25% and Candida species for about 10% of cases of UTI. It is well known that persons practicing intermittent urethral catheterization as a daily routine often have problems with symptomatic UTI.
To this end, and in order to maintain sterility and cleanness of the medical device, medical devices, such as urinary catheters, may be coated with an antimicrobial compound for prevention of bacterial infection. US 2006/0240069, for instance, discloses a use of at least one salt of organic acid(s), and preferably a benzoate or a sorbate, as an antimicrobial agent. Further, WO 00/09173 discloses a stabilized composition having antibacterial, antiviral and/or antifungal activity characterized in that it comprises a silver compound. Light stabilized silver composition can be introduced into catheters or similar medical devices.
For many years silver and silver salts have been used as antimicrobial agents. Silver salts, colloids, and complexes have also been used to prevent and to control infection. For example, colloidal metallic silver has been used topically for conjunctivitis, urethritis, and vaginitis. Other metals, such as gold, zinc, copper, and cerium, have also been found to possess antimicrobial properties, both alone and in combination with silver. These and other metals have been shown to provide antimicrobial behavior even in minute quantities, a property referred to as “oligodynamic.”
Other examples of medical devices having a hydrophilic coating, and an antimicrobial composition such as silver arranged as a separate layer or introduced into the hydrophilic layer, are disclosed in U.S. Pat. No. 7,378,156 and in EP 1 688 470.
However, a problem with known methods of using oligodynamic metals as antimicrobial and antibacterial agent in medical devices is that it is difficult to control the release of the oligodynamic metal ions. If the release rate is too low, the antibacterial properties would be inadequate, and at the same time a too high release rate may be uncomfortable and even harmful for the patient, and also results in a more costly product. In addition, a too high release rate may result in a substantial loss of oligodynamic compound in the wetting solution, again leading to inadequate antibacterial properties in the intended use situation. Accordingly, there is a need for an improved medical device of the above-discussed type, where the release rate of the oligodynamic metal ions can be controlled more accurately.